I'm also a yeti-denier!

With enough proof you can convince the physics community, even if the result is initially weird. My favorite examples are https://en.wikipedia.org/wiki/Wu_experiment and https://en.wikipedia.org/wiki/High-temperature_superconducti... .

I think you can push a little against the magnetic field to rotate and change your orientation, but to gain height the magnetic field is not useful.

[Edit: Mmmm I'd change "but to gain height the magnetic field is not useful." to "but to gain height pushing against the magnetic field is not efficient."]

If it can accelerate forever, thats proof enough for everyone. However violating the conservation of momentum is a Big Deal. Mathematically that shouldn't be possible due to Noether's. The bar to proof is therefore very high.